Thermoplastic polyester resins, mainly polyethylene terephthalate, are widely used for various containers and packaging materials in the form of film and sheet because of their excellent mechanical properties, gas barrier properties, chemical resistance, scent maintenance and hygienic qualities. With the development of blow-molding techniques, especially biaxial orientation blow-molding techniques, these resins are frequently employed for the production of hollow vessels such as bottles.
While such bottles have utility in a wide range of packaging applications, such as containers for soft drink beverages and mouth wash, it would be desirable to extend their utility. For example, utility of bottles consisting of polyester resins for packaging various types of foods is limited because of such resins' barrier properties against oxygen. Providing such bottles with improved barrier properties would reduce exposure of such food products to oxygen, thereby prolonging shelf life.
Various amorphous polyamide compositions and utility thereof in a wide range of applications are well known. Such compositions are generally characterized by a high degree of transparency and lack of a sharply defined melting point. Applications for such compositions include films, sheets, laminates and molded articles. A disadvantage of some of these compositions is their relatively poor thermal properties which limits their utility to relatively low temperature applications.
An example of such a composition, disclosed in U.S. Pat. Nos. 2,715,620 and 2,742,496, is a polyamide of isophthalic acid and hexamethylenediamine. As reported in U.S. Pat. No. 4,250,297, however, such compositions have poor dimensional stability at elevated temperatures. That patent proposed to overcome such difficulties by replacing part of the hexamethylenediamine with an isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine.
Amorphous polyamides based on terephthalic acid and isophthalic acid or their derivatives and hexamethylenediamine also are known as reported in U.S. Pat. No. 3,379,695 and U.S. Pat. No. 3,475,387. While such compositions exhibit improved heat deflection temperatures relative to the isophthalic acid and hexamethylenediamine polyamides, transparency of articles prepared from the compositions suffers and crystallization of the polymer can occur during use of the articles at elevated temperatures if the mol ratio of isophthalic acid to terephthalic acid is too low.
U.S. Pat. No. 2,766,222 discloses transparent compositions prepared from isophthalic acid or isophthalic acid/terephthalic acid mixtures and metaxylylenediamine and that such compositions are suitable for production of molded articles of high transparency, good heat and chemical resistance and excellent tensile and impact strengths. Softening points of 150.degree.-170.degree. C. for such compositions are reported in the examples. It also is disclosed that transparency of the compositions suffers if greater than about 40 mol % isophthalic acid is replaced with terephthalic acid.
U.S. Pat. No. 4,018,746 also is directed to transparent metaxylylenediamine-based compositions, disclosing polyamides prepared from a mixture of straight chain aliphatic diamines of 4-20 carbon atoms and metaxylylenediamine or a mixture of metaxylylenediamine and paraxylylenediamine and a mixture of a saturated aliphatic dicarboxylic acid of 5-20 carbon atoms and at least one aromatic dicarboxylic acid selected from terephthalic acid and isophthalic acid. Aliphatic diamine content of the diamine mixture is said to range from 5-90 mol % and aliphatic acid content of the acid mixture is said to range from 10-90 mol %. The polyamides are said to be useful in preparation of transparent articles such as sheets, plates, tubes, wire coverings and injection molded technical parts.
Utility of metaxylylenediamine group-containing polyamides in molded containers and vessels is disclosed in U.S. Pat. No. 4,398,642 directed to a multi-ply vessel comprising an inner layer of polyester resin, a middle layer composed of a metaxylylene group-containing polyamide resin and an outer layer composed of a synthetic resin having impermeability to moisture. The metaxylylene group-containing polyamide middle layer is said to provide gas barrier properties. However, the glass transition temperature of the metaxylylene polyamide is about 80.degree. C., such that vessels prepared therefrom are susceptible to deformation at elevated temperatures including those to which the vessels may be exposed during hot filling processes.
U.S. Pat. No. 4,535,901 discloses a multi-ply vessel comprising an odd number of layers with the innermost and outermost layers of polyester resin, and at least one middle layer composed of a metaxylylene group-containing polyamide. The middle layer is covered completely by both inner and outer layers to provide good water resistance, high chemical resistance and high hygienic qualities.
It also is known that water absorption lowers the glass transition temperature, Tg, and the crystallization temperature of non-oriented metaxylylene polyamide resin. This effect is observed as a haze in the non-oriented neck portions of multilayer bottles having such resins as the inner gas barrier layer. In areas of monolayer or multi-layer bottles containing metaxylylene/adipic acid polymer with little or no orientation, these areas have a tendency to whiten or become hazy in the presence of moisture. According to a statement in a product bulletin entitled "Toyobo Nylon MXD6" distributed by Toyobo Company, "When non-oriented MXD6 absorbs water from the air, it becomes white. The water absorption lowers glass transition temperature and crystallized temperature, and then makes MXD6 crystallized at room temperature. If the transparency is required for long periods, non-oriented products are not suitable. As far as the multilayer products (PET/MXD6/PET) are concerned the outside layers prevent MXD6 from absorbing water, making crystallization much slower."
U.S. Pat. No. 4,501,781 discloses that a gap may form between the inner surface layer and the intermediate layer resulting in a decrease of transparency of the container. The patent discloses the use of a mixture of polyethylene terephthalate resin and a xylylene group-containing polyamide resin.
Japanese Patent Applications 60-232,952, 60-238,355 and 60-240,452 disclose copolymers of metaxylylenediamine with adipic acid and isophthalic acid containing 30 to 100% isophthalic acid and polyester laminated moldings consisting of a copolymer layer and a polyethylene terephthalate layer.
U.S. Pat. No. 4,728,549 discloses a biaxially oriented multilayered container comprising a wall portion consisting of at least two metaxylylene group-containing polyamide resin layers and one more polyethylene terephthalate layer than the number of metaxylylene group-containing polyamide layers with the terminal portion of the mouth opening being polyethylene terephthalate.
U.S. Pat. No. 4,800,129 discloses thermoformed multilayer structures comprising at least a first and a second layer, the first layer comprising a blend of amorphous polyamides having a Tg greater than about 120.degree. C. and one or more semicrystalline aliphatic polyamide and the second layer comprising a structural thermoplastic resin.
European Patent Application 0 212 339 discloses a method for making a hollow two-layer blow-molded bottle having one layer formed of a biaxially oriented polyethylene terephthalate resin and a second layer formed of a mixture of polyethylene terephthalate resin and 5 to 50 percent by weight of a xylene derivative polyamide resin.
European Patent Application 0 186 154 discloses a nine-layer parison, process for its production and a multilayer container produced from the parison wherein the nine-layer structure is composed of two outside layers and one central layer of polyethylene terephthalate (PET) and two interlayers of a metaxylylenediamine (MXDA) nylon with four adhesive layers of a thermoplastic adhesive resin being positioned between the PET layers and the MXDA nylon layers. This process requires adhesive layers between the PET and MXDA nylon layers.
European Patent Application 0 288 972 discloses a multilayered structure having at least one layer of a copolyamide composed of 55 to 70 mol % of an aliphatic dicarboxylic acid component and 45 to 30 mol % of an aromatic dicarboxylic acid component and a diamine component consisting substantially of metaxylylenediamine. The copolyamides of this patent have relatively high levels of an aliphatic dicarboxylic acid such as adipic acid and use metaxylylenediamine as the diamine component.
U.S. Pat. No. 4,133,802 discloses a biaxially drawn film of a polyamide containing a metaxylylene group which has excellent mechanical and physical properties including a high gas barrier property.
Despite the foregoing, there remains a need for bottles with improved barrier, hot-fill properties and resistance to whitening or hazing upon exposure to moisture and a process for making same.
An object of the present invention is to provide molded bottles having gas properties against oxygen without losing properties of a thermoplastic polyester resin such as excellent mechanical properties, transparency, chemical resistance and the like.
Another object of the present invention is to provide such bottles having excellent dimensional stability and which resists "whitening" upon exposure to moisture.
A further object of the present invention is to provide a molded multilayer bottle having inner and outer layers comprising a thermoplastic resin and at least one intermediate or middle layer comprising a polyamide composition which exhibits improved gas barrier properties, resistance to whitening upon exposure to moisture and ease of processing.
These and other objects and advantages of the present invention will be apparent to those skilled in the art from the following description.
We have now found that the objects of this invention can be obtained by providing bottles comprising a polyamide composition having excellent oxygen barrier properties. Advantageously, such polyamide compositions also are easily melt processed under conditions and with equipment used in the manufacture of PET bottles and thus are well suited for use in making multilayered bottles comprising inner and outer layers of thermoplastics such as PET or polycarbonate and at least one intermediate layer comprising such polyamide compositions. In one embodiment, the bottles comprise a polyamide composition which have glass transition temperatures of 90.degree. C. or greater and oxygen transmission rates of about 2.0 cc-mil/100 in.sup.2 -day-atm or less. The oxygen barrier properties of the invented bottles approach those of bottles having only a metaxylylenediamine polyamide component and the bottles retain excellent clarity even after exposure to high humidity conditions.